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Jurors, Brain Imaging, and the Allure of Pretty Pictures

A picture is worth a thousand words, or so the saying goes.But is it possible for a picture to say more than it should?On the surface, this seems like a silly question.However, in the case of brain imaging and the law, there is gathering evidence that suggests that introducing neuroimaging into the courtroom could perhaps do more damage than good.A series of recent studies suggest that whatever legally probative value brain imaging might have may be outstripped by the tendency of these data to bias the intuitions of the people who are exposed to them.But before examining the results of some of the salient studies, it is worth spending a few moments discussing the legal standards that govern the admissibility of scientific evidence in the courtroom more generally.

The two most salient legal rules in this context are the Federal Rules of Evidence 401 & 403:

·401: “Relevant evidence” means evidence having any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence.

·403: Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by considerations of undue delay, waste of time, or needless presentation of cumulative evidence.

In light of these two rules, the question is:Does the potential probative value of imaging data outweigh whatever potential costs could be associated with their introduction into the courtroom?To see why there may be problems lurking the mist, consider the following four studies:

1.Bright & Goodman-Delahunty (2006):In a series of studies, participants read the verdicts of fictional criminal cases.Some of the participants saw no photographs whereas others either saw neutral photographs (e.g., scratches on a door) or gruesome photographs (e.g., bodily injury).The researchers found that the conviction rate with neutral and gruesome photographs were markedly higher than the conviction rate with no photographs (38%, 41%, and 8.8%, respectively) even though the photos did not add any additional relevant information with respect to the guilt of the alleged perpetrator.These results suggest that photographs could have a biasing effect on jurors’ judgments even when the content of the photographs is not relevant to the task at hand.

2. Gurley and Marcus (2008): Participants were presented with descriptions of violent crimes and asked to determine whether the perpetrators should be found not guilty by reason of insanity.Some participants simply received a description of the crime along with expert testimony that the perpetrator was psychopathic. Other participants received the description of the crime plus one of the following (a) evidence that the perpetrator has a history of brain trauma, or (b) brain images suggesting damage to the frontal lobes. Once again, it appears that brain images made a significant difference. The results suggest that the percentage of participants who judged that the perpetrator was not guilty by reason of insanity was higher when accompanied by a brain image (37%), by testimony concerning brain injury (43%), or by both (50%), than they were when participants received neither (22%).

3.McCabe and Castel (2008):Participants were first presented with articles that included bad arguments—e.g., “watching TV helps with math ability because both activate the temporal lobe.”Whereas some participants received nothing more than the bad arguments, others received the arguments plus either brain images or bar graphs.The results of this study are in line with the results of the two aforementioned studies.Participants who received the supplementary brain images thought the arguments made more sense than the participants who received either supplementary bar graphs or no supplementary images or information (2.9 vs. 2.7 and 2.7, respectively).

4. Weisberg et al. (2008):In a series of studies, participants were asked to distinguish good explanations from bad explanations.In one study, for instance, participants read the following:

Researchers created a list of facts that about 50% of people knew.Subjects in this experiment read the list of facts and had to say which ones they knew.They then had to judge what percentage of other people would know those facts.Researchers found that the subjects responded differently about other people’s knowledge of a fact when the subject themselves knew that fact.If the subjects did know a fact, they said that an inaccurately large percentage of others would know it, too…the researchers call this finding “the curse of knowledge.

After reading this prompt, some participants received an explanation that involved no neuroscience—for instance:

The researches claim this curse happens because subjects make more mistakes when they have to judge the knowledge of others.People are much better at judging what they themselves know.

Other participants, however, received the same explanation in addition to being presented with the following kind of pseudo-neuroscientific information:

Brain scans indicate that this curse happens because the frontal lobe brain circuitry known to be involved in self-knowledge.Subjects make more mistakes when they have to judge the knowledge of others.People are much better at judging what they themselves know.

Despite the fact that this pseudo-neuroscientific information does not add anything to the explanation, participants who were provided with this information found the information more explanatorily satisfying than participants who did not receive this additional information (means = 0.16 and 0.2 and means = -0.73 and -1.1, respectively).

Now is neither the time nor the place to flesh out the results of these interesting studies in detail.My goal is simply to point out some of the evidence which suggests that introducing brain imaging into the courtroom may bias the moral and legal intuitions of judges and jurors—a problem that is further magnified by the fact that laypersons mistakenly assume that fMRI images provide photographs of the brain rather than merely providing complex visually reconstructed statistical correlations.

In light of these worries, we ought to proceed with extreme caution when it comes to the drive to introduce brain imaging into the courtroom.If nothing else, it is clear that steps need to be taken to make sure that the human fondness for pretty pictures doesn’t cloud the ability of judges and jurors to take imaging data at face value.

For more about these studies and the introduction of brain imaging into the courtroom, see:

Aharoni, E., C. Funk, W. Sinnott-Armstrong, & M. Gazzaniga. 2008. Can neurological evidence help courts assess criminal responsibility? Lessons from law and neuroscience. Annals of the New York Academy of Sciences: 1-16.

[…] role that fMRI scans played in Dugan’s sentencing could open the floodgates of a phenomenon speculated about for quite some time: the use of brain imaging in courtrooms. Hughes’ article does a great job […]